Clinical study of radioisotope clearance from the cerebrospinal fluid space using single photon emission computed tomography

Clinical Study of Cerebrospinal Fluid Dynamics Using 111In-DTPA SPECT in Patients With Subarachnoid Hemorrhage

The ventricle-to-background ratio and clearance rate constant measured by indium-111 diethylenetriaminepenta-acetic acid single photon emission computed tomography ((111)In-DTPA SPECT) were evaluated for predicting hydrocephalus in 16 patients at 2 to 3 weeks after onset of subarachnoid hemorrhage. The activity in the lateral ventricles, basal cistern, and hemispheric convexities was measured at 6, 24, and 48 hours after lumbar injection of radionuclide. In the follow-up study, eight patients developed hydrocephalus, and required ventriculoperitoneal shunting. Radioactivity measured in the hemispheric convexity did not reach peak activity within 48 hours. The clearance rate measured by applying the mono-exponential equation failed to show delayed clearance of radionuclide in hydrocephalus. The ratio between the ventricle and basal cistern measured at 6 hours postinjection was the best predictor of hydrocephalus (F(1, 30) = 42.84, p < 0.0001). These results suggest that a single (111)In-DTPA SPECT scan may be sufficient to identify patients at risk of developing hydrocephalus.

Intra-thecal treatment of leptomeningeal lymphoma with immunotoxin

An animal model has been established to investigate the effect of intra-thecal (i.t.) immunotoxins in the treatment of leptomeningeal metastases of acute lymphoblastic leukaemia (ALL). Direct inoculation of L2C lymphoma cells into the cisterna magna of guinea-pigs gives rise to a leptomeningeal pattern of growth, similar to that of human ALL, and to a systemic leukaemia which develops in approximately 14 days. In our model the systemic disease could be controlled with cyclophosphamide while the meningeal disease progressed and provided a target for i.t. immunotoxin. The immunotoxin used consisted of an anti-idiotypic antibody disulphide-bonded to the ribosome-inactivating protein saporin. It was highly cytotoxic to L2C cells in vitro, being around 30,000 times more potent than a control immunotoxin at inhibiting protein synthesis. In vivo, the maximum tolerated dose of i.t. immunotoxin was 10 micrograms. From the rate at which radiolabelled immunotoxins appeared in the plasma following i.t. injection, we were able to estimate that its half-life in the cerebrospinal fluid (CSF) was between 1 1/2 and 2 hr. Intrathecal treatment of guinea-pigs with immunotoxin 1 day after inoculation of L2C cells into the cisterna magna had a remarkable therapeutic effect. All guinea-pigs treated with 0.5 or 5 micrograms of immunotoxin survived, and remained tumour-free for more than 100 days after treatment, while control animals given cyclophosphamide alone or an irrelevant immunotoxin had a mean survival time of 28 days. Provided concerns over toxicity can be overcome, these results indicate that i.t. immunotoxins offer an alternative, highly specific form of treatment in leptomeningeal neoplasia.